Orthogonal uplink transmission schemes such as Orthogonal Frequency Division Multiplexing (OFDM), single carrier Frequency Division Multiple Access (FDMA) or distributed FDMA such as interleaved FDMA with multiple terminals will become increasingly important e.g. for future evolutions of air interfaces for mobile radio systems. These radio systems are currently under discussion e.g. in Third Generation Partnership Project (3GPP) Technical Specification Group (TSG) Radio Access Network (RAN), for Wireless Local Area Networks (WLANs) e.g. according to standard IEEE 802.11a, or for a 4th generation air interface.
Given the licensed bandwidth, transmission capacity from network providers e.g. for picture uploading or video communication has to be as high as possible for all users to serve as many subscribers as possible. Further the quality of service experienced by the user and especially the coverage of the service is an important property demanded by the user. So an uplink access scheme shall work well at the cell borders of a single frequency network (SFN).
In cellular systems with a frequency reuse factor of 1 the signal to interference ratio at the cell border can approach the factor 1 or 0 dB, so that no useful transmission from a mobile terminal to the base station can be kept up if a mobile terminal from a neighboring cell is near to the considered mobile terminal and sends with the same power on the same frequencies.
Therefore in CDMA (CDMA=Code Division Multiple Access) a soft handover exists and the mobile terminals always use a different (terminal specific) scrambling code in the uplink. The reception is then possible using the spreading gain from CDMA. As is known due to the strong interference the uplink capacity is considerably limited.
In OFDM transmission, frequency groups are allocated to a mobile terminal instead of codes in CDMA transmission. In other FDMA orthogonal uplink schemes, frequencies are also allocated in the uplink to a mobile terminal. So in these schemes in contrast to CDMA transmission, interference can be planned and avoided. For these orthogonal uplink transmission schemes the problem at the cell border has to be solved as well.
Up to now, frequency planning for the cells is possible by means of giving each whole cell a distinct frequency band.
However, frequency distribution to the different cells reduces the available uplink resources per cell very considerably e.g. by a factor of ⅓ or 1/7 and thus the overall system throughput. It is a waste of resources for the inner area of a cell.
A frequency reuse of e.g. ⅓ only in the outer part of the cell is possible but still wastes too much resources.